"The finding may have important implications in regenerative and reproductive medicine," say Wu and colleagues.

Two other scientists, unrelated to the study, say the results are interesting but need independent confirmation.

Wu and team say they isolated female germline stem cells (FGSCs) from the ovaries of five-day-old and adult mice.

They say the cells were cultured for more than six months and then transplanted into the ovaries of infertile female mice.

Of these mice, 80% went on to produce offspring after natural mating, say the researchers.

"These results suggest that oocytes can be regenerated in sterile recipient females by transplantation of FGSCs," they write.

Overcoming infertility?

Scientists generally believe that the production of eggs, known as oocytes, stops before birth for most species of mammals, including humans.

"Sperm are produced continuously in men but the number of eggs in women is fixed at birth," says Professor Azim Surani, an expert in physiology and reproduction at the University of Cambridge's Gurdon Institute, who is not connected to the study.

"This new study in mice now suggests that there are also stem cells present in ovaries that can be cultured in a dish, which upon transfer to ovaries can develop into viable eggs and give rise to offspring," he says.

"This finding, if confirmed independently, could advance understanding of these ovarian stem cells and advance research on female infertility."

Another researcher, also independent from the study, calls for caution.

"A lot more work is needed to understand what these new cells really are, and to verify the findings and the claims," says UK stem cell expert Professor Robin Lovell-Badge at the MRC National Institute For Medical Research.